1. Field of the Invention
The present invention relates to a mold cased circuit breaker (MCCB), and particularly, to an MCCB having a plurality of single pole breaking units for a plurality of electrical poles, and configured to simultaneously open or close the single pole breaking units by a pair of common shaft pins, the MCCB capable of transmitting a torque for opening or closing contacts to adjacent single pole breaking unit with a minimized loss, and capable of preventing the shaft pins from being bent.
2. Background of the Invention
A mould cased circuit breaker (MCCB) is a low-voltage electrical device that supplies electrical power to a circuit in a normal state, but interrupts the circuit when an abnormal current such as an electric shortage current occurs.
The conventional MCCB comprises single pole breaking unit provided for each of Alternating Current 3 poles of R pole, S pole and T pole (in other words 3 phases), each single pole breaking unit including a movable contactor, fixed contactors, a shaft for rotatably supporting the movable contactor, and an arc extinguishing unit mounted in an insulated case; a pair of shaft pins (shaft driving pins) penetratingly installed at the shafts inside the plurality of single pole breaking units for simultaneously opening or closing the plurality of single pole breaking units; and a switching mechanism including a trip spring, a latch, and links for providing an opening/closing driving force to the shaft pins. Here, the plurality of single pole breaking units, the pair of shaft pins, and the switching mechanism are mounted in a mold case having a lower case and an upper cover. The reason why the single pole breaking units for a plurality of poles configured is in order to minimize the mold cased circuit breaker with the same capacity by ensuring an insulated state among the electrical poles by mounting the single pole breaking units in each insulated case, and by reducing an insulated distance among the poles.
In a mold cased circuit breaker for four poles of R, S, T and N, sequentially and including single pole breaking units, the switching mechanism is installed at the single pole breaking units of ‘S’ pole. And, a driving force to open or close contacts is directly transmitted to one of the pair of shaft pins, thereby rotating a shaft connected to the shaft pin. Since the other shaft pin is driven to follow the driving shaft pin, a very small difference occurs between rotation moments of the pair of shaft pins. The small difference causes one shaft connected to the shaft pins and disposed in the single pole breaking unit to transmit a rotation force to its adjacent shaft with an eccentric state. Furthermore, the small difference causes the movable contactors and the fixed contactors inside the single pole breaking units to be contacted to or separated from each another with a low reliability.
The difference between rotation moments of the pair of shaft pins is more severe at a part of the pair of shaft pins between the single pole breaking unit for ‘S’ pole where the switching mechanism is installed, and the single pole breaking unit for ‘N’ pole farthest from the single pole breaking units for ‘S’ pole. The large difference causes the shaft pins to be bent. And, the bent state of the shaft pins lowers a reliability to simultaneously open or close the plurality of single pole breaking units of the mold cased circuit breaker.